A semiconductor integrated circuit may be in need of a voltage level shifter for an interface between circuits requiring different voltage levels. For example, an integrated chip including a semiconductor or the like is generally operated within a predetermined voltage level range, but may need a signal voltage beyond the predetermined voltage level range in order to interface with external systems or to transmit a signal to other systems. In this case, a level shifter is placed between the two systems so as to connect the two systems requiring different signal voltage levels. Such a level shifter is particularly used for shifting the level of the signal voltage from a low voltage level range into a high voltage level range.
A conventional level shifter comprises first and second transistors of a P-metal oxide semiconductor (PMOS) type. The first transistor is connected between a first power line and an output terminal, and the second transistor is diode-connected between the output terminal and a second power line.
In the conventional level shifter, when a low level input voltage is inputted to a gate electrode of the first transistor, a high level output voltage is produced depending on an on-resistance ratio between the first and second transistors.
Further, when a high level input voltage is inputted to the gate electrode of the first transistor, a low level output voltage is increased to be higher than the low level by a threshold voltage (Vth) of the second transistor, that is, increased into (LVSS+|Vth|). Where, LVSS is a low level voltage supplied from the second power line.
However, the conventional level shifter consumes relatively more power because of leakage current due to static current of the second PMOS transistor.
Further, the conventional level shifter is not capable of adjusting the level of the output voltage, because the low level output voltage can only be increased to be higher than the low level input voltage by only the threshold voltage (Vth) of the second transistor.